1. Field of Invention
The present invention relates to a device that corrects uneven color of an image that is projected by a projector that includes a projection lens with a zoom function. The invention also relates to a method of correcting uneven color of such a projected image.
2. Description of Related Art
A related art projector (projection type display apparatus) is a type of image display apparatus that projects and displays an image, which is formed on a display device, such as a liquid crystal panel, digital micromirror device (DMD: registered trademark of Texas Instruments), and CRT, for instance, on a screen through a projection lens. For example, a transmission type liquid crystal projector is arranged such that a light beam from a light source is modulated according to an image signal transmitted through a liquid crystal panel, and an image formed by the modulation is projected and displayed on a screen through a projection lens. A lens with a zoom function is ordinarily utilized as a projection lens of the projector in order to enlarge and reduce an image projected on the screen within a predetermined range.
It is preferable that a projected image displayed on a screen be uniform without uneven color. Actually, however, uneven color often occurs in a projected image due to the dispersion, for example, in the input/output characteristics of a display device, such as a liquid crystal panel, in the electric characteristics of a signal processing circuit of an image signal, and in the optical characteristics of an optical system.
Thus, an uneven color correction circuit is mounted on a related art projector to correct the image data of a pixel in which uneven color occurs so as to suppress uneven color. Uneven color correction data for correcting image data is determined, for example, as described below. First, a uniform image of halftone (hereinafter “solid image”), typically, a gray solid image is projected and displayed, and the projected image being displayed is photographed with a video camera or the luminance of the projected image is measured with a luminance meter, thereby measuring the distribution of the uneven color of the projected image. Next, appropriate uneven color correction data is determined by repeating the adjustment of the image data of a pixel in which uneven color occurs and the measurement of the uneven color which occurs in the projected image of the image data after the adjustment. The thus obtained correction data is previously stored in a ROM, and the uneven color correction circuit corrects the image data with reference to the uneven color correction data.